Strain mapping in nanowires
ABSTRACT A method for obtaining detailed two-dimensional strain maps in nanowires and related nanoscale structures has been developed. The approach relies on a combination of lattice imaging by high-resolution transmission electron microscopy and geometric phase analysis of the resulting micrographs using Fourier transform routines. We demonstrate the method for a germanium nanowire grown epitaxially on Si(111) by obtaining the strain components epsilon(xx), epsilon(yy), epsilon(xy), the mean dilatation, and the rotation of the lattice planes. The resulting strain maps are demonstrated to allow detailed evaluation of the strains and loading on nanowires.
SourceAvailable from: C. G. Garay-Reyes[Show abstract] [Hide abstract]
ABSTRACT: Elastic strains, caused by GP zones in an aged Al alloy, were determined quantitatively using two techniques: Dark Field In-line Holography (DFH) and High Resolution Transmission Electron Microscopy-Geometric Phase Analysis (HRTEM-GPA). The results obtained by both techniques showed that the elastic strain was not uniform along the precipitate–matrix interface. In some areas, it was found that strain had negligible value and this was attributed to the loss of coherence between the lattices. It is suggested that a possible explanation for this fact could be a variation in the “vacancies pump mechanism” kinetics. To obtain a better interpretation of the experimental deformation maps, a reference GP precipitate–matrix structure was built using QSTEM software. The main advantages of DFH over HRTEM-GPA were a bigger field of view and low electron dose requirements without spatial resolution loss. Another difference found was that crystalline defects such as dislocations were evidenced by HRTEM-GPA in contrast to the result obtained by DFH. However, strain measurements were affected by mask size effect in the former.Materials Characterization 11/2012; 73:61–67. DOI:10.1016/j.matchar.2012.07.017 · 1.93 Impact Factor
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ABSTRACT: Cu nanotwin particles were successfully obtained on SiO2 films through Ar ion beam to bombard the copper transmission electron microscopy (TEM) grid. The structural rearrangement of a large Cu nanotwin particle was observed in situ using high-resolution TEM under long-time electron beam irradiation. The rotation of the whole nanotwin particle was also observed. The Cu nanotwin particle possessed some independent subgrains. The crystal facets of the subgrains tended to be parallel to each other after rearrangement during electron beam irradiation. The deformation of the Cu nanotwin particle started from the central subgrains to the side subgrains. Structural rearrangement in single subgrain occurred in the opposite direction, from outside to inside. Strain fields in Cu nanotwin particle was mapped using geometric phase analysis, which displayed the decrease in the space between crystal facets and the change from tensile strain to compressive strain.Micro & Nano Letters 07/2012; 7(7):676-678. DOI:10.1049/mnl.2012.0295 · 0.80 Impact Factor
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ABSTRACT: Thanks to their unique morphology, nanowires have enabled integration of materials in a way that was not possible before with thin film technology. In turn, this opens new avenues for applications in the areas of energy harvesting, electronics and optoelectronics. This is particularly true for axial heterostructures, while core-shell systems are limited by the appearance of strain-induced dislocations. Even more challenging is the detection and understanding of these defects. We combine geometrical phase analysis with finite element strain simulations to quantify and determine the origin of the lattice distortion in core-shell nanowire structures. Such combination provides a powerful insight in the origin and characteristics of edge dislocations in such systems, and quantifies their impact with the strain field map. We apply the method to heterostructures presenting single and mixed crystalline phase. Mixing crystalline phases along a nanowire turns out to be beneficial for reducing strain in mismatched core-shell structures.Nano Letters 02/2014; DOI:10.1021/nl4046312 · 12.94 Impact Factor